couldn't mount because of unsupported optional features (4000400)

[Sjoerd Mullender]

On 04/20/2007 10:24 PM, Anthony J Placilla wrote:
> Sjoerd Mullender wrote:
>> On 04/20/2007 08:50 PM, Anthony J Placilla wrote:
> 
> dumpe2fs /dev/hdc1 | grep Backup
> 
> It'll give output something like this:
> (NB this is *my* box. Your's will be different)
> 
> root at aplacilla ~]# dumpe2fs /dev/sda1 | grep Backup
> dumpe2fs 1.39 (29-May-2006)
>   Backup superblock at 8193, Group descriptors at 8194-8194
>   Backup superblock at 24577, Group descriptors at 24578-24578
>   Backup superblock at 40961, Group descriptors at 40962-40962
>   Backup superblock at 57345, Group descriptors at 57346-57346
>   Backup superblock at 73729, Group descriptors at 73730-73730
> 
> then do
> 
> e2fsck -b 8193 /dev/hdc1
> 
> 
> obviously you'll need to adjust the argument to -b with a listed backup
> superblock

Unfortunately:

# dumpe2fs /dev/hdc1 | grep Backup
dumpe2fs 1.39 (29-May-2006)
dumpe2fs: Filesystem revision too high while trying to open /dev/hdc1
#

But this gave me an idea: I hadn't saved the list of backup superblocks
when I first created the file system, but I figured that mke2fs might
have an option to tell me.  So:

# mke2fs -n -j /dev/hdc1
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
4889248 inodes, 9767512 blocks
488375 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
299 block groups
32768 blocks per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632,
2654208,
        4096000, 7962624

#

And indeed, using the first backup I am now able to check the file
system.  There weren't a huge number of errors (only errors of the type
Free inodes count wrong for group #X) and the check succeeded.  I can
now mount the file system again.

Thanks for the help.

-- 
Sjoerd Mullender